1. Field of the Invention
The present invention generally relates to an auxiliary heat-insulating jig, and more specifically, it relates to an auxiliary heat-insulating jig improved to be capable of increasing an adiabatic effect. The present invention also relates to a method of manufacturing an auxiliary heat-insulating jig improved to increase an adiabatic effect. The present invention further relates to a vertical heat treatment apparatus having such an auxiliary heat-insulating jig.
2. Description of the Prior Art
A semiconductor device such as a MOS-LSI or a bipolar LSI is fabricated through a number of heat treatment steps such as an oxidation step, a CVD step and a diffusion step. Following the recent progress of the semiconductor device fabrication technique, a general process apparatus is mainly formed by a single wafer processing apparatus. On the site of production, about 25 silicon wafers for forming semiconductor devices are generally treated as a single lot. Thus, the single wafer processing apparatus treats and physically distributes silicon wafers lot by lot.
On the other hand, a vertical heat treatment apparatus requiring a long treatment time generally treats and physically distributes at least 100 silicon wafers, i.e., at least four lots of silicon wafers at a time, while a vertical heat treatment apparatus called a high-temperature heat treatment furnace capable of reducing the treatment time can treat and physically distribute a lot of silicon wafers at a time.
When a vertical heat treatment apparatus such as a vertical transformation CVD (chemical vapor deposition) furnace is employed in heat treatment steps, silicon wafers for forming semiconductor devices are loaded on a vertical heat treatment wafer boat of quartz or SiC and inserted into a reaction tube of the vertical heat treatment apparatus. A number of silicon wafers can be vertically loaded on the vertical heat treatment wafer boat at proper intervals in a horizontally kept state. In this case, the vertical heat treatment wafer boat is generally set on a heat-insulating jig referred to as a heat-insulating cylinder.
This heat-insulating jig is set between the vertical heat treatment wafer boat and a cap (a component serving as the lid of the reaction tube during heat treatment). The heat-insulating jig prevents heat in the reaction tube from escaping from a throat by thermal conduction while preventing a sealing member for the cap and a rotation mechanism of the wafer bat from deterioration or breakage caused by radiant heat. Therefore, a heat-insulating cylinder having large thermal capacity is employed in a high-temperature vertical heat treatment furnace.
The heat-insulating cylinder may be provided in various shapes. Referring to FIG. 37, for example, an opaque quartz cylinder 324 stores an insulator 323 prepared by deairing a quartz capsule 321 and sealing the same with flocculently rounded quartz wool 322. This opaque quartz cylinder 324 is generally applied to a furnace of a relatively high-temperature specification.
Referring to FIG. 38, a heat-insulating jig formed by vertically arranging several opaque quartz discs of about 5 mm in thickness at intervals of several cm is also known.
Referring to FIG. 39, an opaque quartz cylinder 392 storing several vertically arranged opaque quartz discs 391 is also proposed.
Referring to FIG. 40, a large cylinder 401 storing alternately stacked discs 7 and cylinders 36 (not welded) is also known.
FIG. 41 shows a low-temperature heat-insulating cylinder set on a boat. FIG. 42 shows a high-temperature heat-insulating cylinder set on a boat. The heat-insulating cylinder shown in FIG. 41 is applied to a furnace employed at a relatively low temperature, and the heat-insulating cylinder shown in FIG. 42, prepared from that shown in FIG. 37, is applied to a furnace employed at a relatively high temperature.
While opaque quartz is the optimum material for the heat-insulating cylinder, transparent quartz may be additionally employed as an auxiliary material.
A material prepared by storing a silicon wafer in a deaired or nitrogen-sealed quartz glass member for preventing the silicon wafer from oxidation is also proposed as an insulator. This material, proposed on the basis of such a supposition that the silicon wafer having a mirror-finished surface may reflect approximately 100% of radiant heat, reflects visible light. However, the material absorbs infrared light and the silicon wafer is immediately heated to cause heat radiation again, and hence this material is improper for application to an insulator.
Some materials of silicon carbide (hereinafter referred to as SiC) are proposed as ideas. However, it is to be noted that the thermal conductivity of SiC is 45 to 125 W/m.k, i.e., at least 20 to 60 times that of quartz glass. SiC must be regarded as a remarkably excellent thermal conductor, and an expression xe2x80x9cinsulating or heat-shielding plate of SiCxe2x80x9d means xe2x80x9cheat-shielding plate having excellent thermal conductivityxe2x80x9d in other words. This expression is unsubstantial and misleading wording confusing users similarly to xe2x80x9cinsulator excellently conducting electricityxe2x80x9d, since SiC has no heat-shielding effect in practice. A thin plate of SiC used in any of the aforementioned ideas may be used not for heat shielding but for a purpose of attaining an effect of rectifying reaction gas, for example, and must have a more proper name than a heat-shielding plate. For example, the thin plate of SiC may be properly referred to as a rectifying plate or a dummy wafer. In a vertical heat treatment apparatus, SiC having excellent thermal conductivity is mainly employed as the material for a soaking pipe.
Recently, a general vertical heat treatment apparatus having a track temperature increase speed of not more than 8xc2x0 C./min. and a track temperature reduction speed of not more than 3xc2x0 C./min. is being replaced with a vertical heat treatment apparatus, referred to as a high-speed temperature-control furnace, having a track temperature increase speed of at least 45xc2x0 C./min. and a track temperature reduction speed of at least 15xc2x0 C./min.
Such a high-speed temperature-control furnace employs a heat-insulating jig having small thermal capacity so that the temperature control speed is not reduced.
When such a heat-insulating jig is employed, heat escapes from a bottom area of a wafer boat in a temperature region exceeding 1000xc2x0 C. Therefore, the heat-insulating jig requires a long time for reaching a target temperature exceeding 1000xc2x0 C. and entering a stable state.
Also in a range where the heat-insulating jig can reach the target temperature, heat escapes from a portion around the bottom, and hence a heater for the bottom portion is regularly in a state substantially at full power. Therefore, thermal stress is applied to a wafer treated in the vicinity of the bottom, to cause crystal defects called slips in the wafer.
For example, Japanese Patent Laying-Open No. 9-74071 (1997) proposes a heat-insulating jig formed by arranging a plurality of thin heat-shielding plates as a heat-insulating jig capable of reducing thermal capacity. The material for this heat-insulating jig is SiC. As to employment of quartz, the gazette shows such a negative view that quartz may be selected if the thickness of a quartz member can be technically reduced.
As described above, SiC absorbing infrared rays and having excessively small thermal capacity has a small adiabatic effect. Therefore, SiC cannot be used as a heat-shielding material even in a furnace of a relatively low-temperature specification such as a CVD furnace. In other words, radiant heat (transmitted radiant heat and re-radiation) and heat conduction from a material referred to as a heat-shielding plate of SiC disadvantageously deteriorate or disappear a sealing member of a heat treatment furnace or break down a rotation mechanism of a wafer boat.
The inventors have reached an idea of adding an auxiliary heat-insulating jig to a heat-insulating jig employed in a general furnace of an intermediate temperature specification, in order to improve an adiabatic effect. As means of suppressing increase of thermal capacity with an excellent adiabatic effect, the inventors have noted the aforementioned heat-insulating jig shown in FIG. 38 formed by vertically arranging several opaque quartz discs at intervals.
Quartz glass absorbs light of 2200 nm and 2700 nm in wavelength resulting from OH groups present therein. However, quartz glass hardly absorbs light of other wavelengths up to an infrared region of 3400 nm. In the field of optical communication employing infrared rays of 1.55 xcexcm in wavelength, therefore, quartz glass is employed as the material for an optical fiber member serving as a transmission medium.
Heat is shielded through reflection of light on a surface due to the difference between the refractive indices of an in-furnace atmosphere and quartz glass. Opaque quartz glass including small bubbles therein has a larger surface area contributing to reflection than transparent quartz glass. Therefore, opaque quartz glass is widely employed as an insulator.
The heat-insulating jig shown in FIG. 38 is not for a high temperature. When a plate insulator of 5 mm in thickness, for example, is divided into plates of 1 mm in thickness, however, the surface area is increased to about five times in outline while thermal capacity remains unchanged. The inventors have considered that a number of such thin plate insulators may be employed in a high-temperature region when superposed with each other. The inventors have also considered that a space capable of receiving an auxiliary heat-insulating jig is limited and hence an auxiliary heat-insulating jig having a high adiabatic effect can be obtained by reducing the intervals between the plate insulators as compared with those in the prior art while leaving the thermal capacity intact. However, the following problems have been recognized in relation to preparation of such an auxiliary heat-insulating jig:
When reduced in thickness, heat-insulating quartz discs are deformed by their own weight during high-temperature treatment. In order to prevent such deformation, therefore, supports for the heat-insulating quartz discs are preferably set up in the vicinity of points minimizing the moments of the discs and welded to the discs. However, the intervals between the discs are so small that a welding tool cannot reach welded portions. Therefore, the supports and the discs cannot be welded to each other.
When the supports are arranged on the outer sides of the discs and welded to the discs, the discs must be warmed by a burner in welding so that quartz glass is not cracked. However, necessary portions cannot be sufficiently warmed due to the narrow intervals, and quartz glass is cracked if the supports and the discs are forcibly welded in such a situation. Therefore, the supports and the discs cannot be welded to each other in this case either.
Even if the intervals between the discs are increased for enabling welding, there is a high possibility that the thin quartz glass discs are immediately cracked when broiled with the burner. In order to warm the thin discs with the burner, therefore, sophisticated skill or specific equipment as well as a high cost are required while the yield is reduced in this case. When plate insulators are reduced in thickness, further, thermal deformation or breakage is readily caused to reduce the endurance time.
A conceivable method of manufacturing an auxiliary heat-insulating jig as compactly as possible within the conventional technical range is described with reference to FIGS. 43 to 46.
Referring to FIGS. 43 to 46, spacers 9 and plate insulators 7 are first prepared in necessary numbers.
Referring to FIG. 43, three supports 6 are vertically set up on a bottom plate 8, to be welded and fixed to the bottom plate 8 with an oxyhydrogen burner 17.
As shown in FIG. 44, lowermost spacers 13 are engaged with the supports 6. The lowermost spacers 13 are provided with holes for receiving the supports 6. The inner sides of the holes provided in the lowermost spacers 13 are tapered (not shown), not to interfere with portions connecting the bottom plate 8 and the supports 6 with each other.
Referring to FIG. 45, the lowermost plate insulator 7 is engaged with the supports 6, for receiving the spacers 9 thereon. The plate insulator 7 and the spacers 9 are also provided with holes for receiving the supports 6 respectively. Thus, the plate insulators 7 and the spacers 9 are alternately engaged with the supports 6 by necessary numbers, so that the supports 6 and a top plate 18 are welded to each other with the oxyhydrogen burner 17 after the uppermost plate insulator 7 is engaged with the supports 6, as shown in FIG. 46. Thereafter annealing is performed for removing strain caused during welding. FIG. 46 shows the final shape of the auxiliary heat-insulating jig.
Referring to FIG. 46, the interval between the top plate 18 and the uppermost plate insulator 7, which must be welded to each other with the burner 17, cannot be further reduced.
The inventive heat-insulating jig, to be inserted between an existing heat-insulating jig and a boat, is limited in settable height and hence no unnecessary space must be left.
The heat-insulating cylinder shown in FIG. 42 employing the heat-insulating jig shown in FIG. 40 has a possibility of thinly forming the plate insulators 7 and the spacers 36 provided inside the heat-insulating cylinder and stacking a number of plate insulators 7. In this case, however, the number of the stacked plate insulators 7 is increased, leading to unstableness. Therefore, a wafer boat set on the heat-insulating cylinder may disadvantageously fall, and hence this structure cannot be employed in consideration of safety.
The apparatus also has its own problem. A high-speed temperature-control furnace cannot perform treatment at 1100xc2x0 C. Therefore, a step of recovering crystal defects or the like by annealing requires heat treatment at a temperature of at least 1100xc2x0 C. for about 60 minutes. However, a general diffusion furnace requires a long time for temperature control, leading to a long treatment time. In order to maintain the throughput, therefore, the high-speed temperature-control furnace treats a plurality of lots at a time. However, the high-speed temperature-control furnace transfers the treated substances lot by lot in all of the remaining steps, leading to inferior production balance.
The present invention has been proposed in order to solve the aforementioned problems, and an object thereof is to provide an auxiliary heat-insulating jig necessary for producing a high-speed temperature-control furnace capable of performing high-temperature treatment.
Another object of the present invention is to provide an auxiliary heat-insulating jig capable of preventing plate insulators from breakage caused by welding and improving assembling workability.
Still another object of the present invention is to provide an auxiliary heat-insulating jig reducing the thickness of plate insulators to the level of the thickness of wafers, exhibiting small increase of thermal capacity and having a high adiabatic effect.
A further object of the present invention is to provide an auxiliary heat-insulating jig withstanding a high temperature, having a structure not thermally deforming thin plate insulators.
A further object of the present invention is to provide a method of thinly finishing plate insulators to the level of the thickness of wafers.
A further object of the present invention is to provide a wafer boat provided with plate insulators by mounting thin plate insulators on the wafer boat so that the wafer boat itself has an adiabatic function.
A further object of the present invention is to provide a vertical heat treatment apparatus capable of treating and operating all devices in semiconductor device fabrication steps lot by lot in a physical distribution unit and improved to be capable of increasing productivity of a total factory.
A further object of the present invention is to provide a modification method for obtaining such a vertical heat treatment apparatus.
A further object of the present invention is to provide a method of fabricating a semiconductor device with such a vertical heat treatment apparatus.
An auxiliary heat-insulating jig according to a first aspect of the present invention is provided between a wafer boat and a heat-insulating jig in a vertical heat treatment apparatus comprising the wafer boat and the heat-insulating jig. This auxiliary heat-insulating jig comprises a plurality of vertically arranged plate insulators. The aforementioned plate insulators are made of opaque quartz.
According to a preferred embodiment of the present invention, the auxiliary heat-insulating jig comprises a base and a plurality of supports vertically set up on the aforementioned base. Fixing means are provided on the respective ones of the aforementioned plurality of plate insulators for fixing the plurality of plate insulators in association with the aforementioned supports. A spacer is detachably inserted between each pair of the aforementioned plurality of vertically arranged plate insulators for defining a clearance therebetween.
According to another preferred embodiment of the present invention, the aforementioned fixing means include:
(a) through holes vertically passing through the aforementioned plate insulators,
(b) U-shaped notches provided on the outer peripheral portions of the aforementioned plate insulators for receiving side portions of the aforementioned supports,
(c) semicircular notches provided on the outer peripheral portions of the aforementioned plate insulators for receiving side portions of the aforementioned supports, or
(d) rectangular notches provided on the outer peripheral portions of the aforementioned plate insulators for receiving side portions of the aforementioned supports.
According to still another preferred embodiment of the present invention, the thickness of the aforementioned plate insulators is rendered substantially identical to the thickness of a semiconductor substrate. The thickness of the aforementioned plate insulators is rendered substantially identical to the thickness of a semiconductor substrate, whereby the surface areas of the plate insulators are increased with respect to the volumes, for increasing reflectivity for infrared rays.
According to a further preferred embodiment of the present invention, reinforcing parts reinforcing the aforementioned plate insulators are provided on at least single surfaces of the plate insulators, and the aforementioned reinforcing parts are integrally formed with the aforementioned plate insulators.
According to a further preferred embodiment of the present invention, the aforementioned reinforcing parts include:
(a) portions, having a larger thickness than the remaining portions, radially extending from the central portions of the aforementioned plate insulators, and/or
(b) portions, having a larger thickness than the remaining portions, forming circumferences apart from the central portions of the aforementioned plate insulators.
According to a further preferred embodiment of the present invention, the auxiliary heat-insulating jig further comprises a base, a plurality of supports vertically set up on the aforementioned base and fixing means provided on the respective ones of the aforementioned plurality of plate insulators for fixing the plurality of plate insulators in association with the aforementioned supports. The aforementioned plurality of plate insulators are engaged into the auxiliary heat-insulating jig through the aforementioned fixing means, to be fixed.
An auxiliary heat-insulating jig according to a second aspect of the present invention is mounted on a wafer boat. The aforementioned wafer boat comprises a support provided on its side wall with a plurality of vertically arranged first notches for receiving semiconductor substrates in the first notches and supporting the semiconductor substrates. This auxiliary heat-insulating jig comprises a plurality of vertically arranged plate insulators having a thickness rendered substantially identical to the thickness of the aforementioned semiconductor substrates and provided with reinforcing parts on at least single surfaces thereof. Second notches are provided on the outer peripheral portions of the aforementioned plate insulators for receiving an extension part of the aforementioned support to be capable of fixing the aforementioned plurality of plate insulators by engaging the aforementioned second notches in first notches provided in the extension part of the aforementioned support.
A wafer boat provided with plate insulators according to a third aspect of the present invention has an auxiliary heat-insulating jig mounted thereon. The aforementioned auxiliary heat-insulating jig includes a plurality of vertically arranged plate insulators. The aforementioned plate insulators are made of opaque quartz.
A vertical heat treatment apparatus according to a fourth aspect of the present invention comprises a wafer boat having an auxiliary heat-insulating jig mounted thereon. The aforementioned auxiliary heat-insulating jig includes a plurality of vertically arranged plate insulators. The aforementioned plate insulators are made of opaque quartz.
A vertical heat treatment apparatus according to a fifth aspect of the present invention comprises a wafer boat having an auxiliary heat-insulating jig mounted thereon. The aforementioned auxiliary heat-insulating jig includes a plurality of vertically arranged plate insulators. The aforementioned plate insulators are made of opaque quartz.
In a method of manufacturing an auxiliary heat-insulating jig according to a sixth aspect of the present invention, a rectangular block made of quartz glass is first prepared. A quartz glass plate is cut out from the aforementioned rectangular block. The aforementioned quartz glass plate is polished for forming a thin plate insulator.
A method of modifying a vertical heat treatment apparatus according to a seventh aspect of the present invention is a method of modifying a high-speed temperature-control heat treatment apparatus of an intermediate temperature specification to a high-speed temperature-control heat treatment apparatus of a high-temperature specification. This method employs a wafer boat provided with plate insulators. The aforementioned wafer boat provided with plate insulators has an auxiliary heat-insulating jig mounted thereon. The aforementioned auxiliary heat-insulating jig includes a plurality of vertically arranged plate insulators. The aforementioned plate insulators are made of opaque quartz.
A method according to an eight aspect of the present invention is a method of fabricating a semiconductor device employing the vertical heat treatment apparatus having the aforementioned characteristics.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.